Efficient use of electricity is paramount to society today due to demand that continues to increase through the electrification of the world at a pace that is outstripping the ability of the planet to generate the required energy. To combat this, regulations have been introduced to improve the efficiency of power supplies used to convert AC voltages to the DC voltages used by today's sophisticated electronic equipment.
Electronic devices are typically supplied with power from a power supply that converts AC line power to a DC voltage. However, various components in the electronic devices may require different DC voltages from that supplied by the power supply. In addition, some of these components require a highly regulated voltage to operate properly. DC to DC converters are used to convert the output of the power supply to a different regulated voltage.
Examples of electronic devices which typically use DC to DC converters are computers, servers, radios and like equipment. For example, in a computer the power supply unit may produce one voltage, for example, 10 volts, for components such as disc drives while another lower voltage, such 3 or less volts, is needed to supply processors and memory chips. In the case of computers, it is important that these lower voltage levels be maintained as precisely as possible since the logic circuitry depends upon voltage levels for accuracy. This is true even when high current demands are being placed upon the main power supply for instance during startup or whenever disc drives spin up from sleep mode and impose transient draws upon the power supply.
First generation resonant converters have successfully been used to meet the energy star requirements above in the high volume desktop and notebook computer fields. These first generation converters utilize fixed frequency resonant DC-to-DC stages to efficiently convert power to the load, but require an amplitude modulation stage to remove ripple and tighten the load regulation. These extra circuits add cost and size to the assembly. Since the power factor of the AC input waveforms must also meet stringent standards, the prior art converter has the burden of having three stages to complete the transfer of energy from an AC line to the end DC load; A power factor stage in the front, an amplitude modulation stage second and a final fixed frequency DC to DC converter for the main step down of voltage.
It is, therefore, one of the primary objects of the present invention to remove the second amplitude modulation stage of the current high volume resonant mode power supplies and frequency modulate the resonant converter while still being able to operate the resonant mode converter with synchronous power field effect transistors (“FETS”) for optimum efficiency.